Have you even watched Star Trek? If it wasn't for Picard's double fist poundings even the Ferengi could have conquered Star Fleet.
You should read TV Tropes. Things like "The Worf Effect" or "Plot-Induced Stupidity".
I don't care about when MACO's were seen last, in soft canon there are newer organisations like the Starfleet Rangers for example. The problem with MACO-characters is that they could only play half of the game. They are pure ground troops. Having a MACO captain a starship is even crazier than a freshly promoted lieutenant. So I agree. Play a tactical captain, put him in a MACO like uniform, and if you really want make an away team separate from your bridge crew in similar uniforms.
According to the book, which was written with cryptic studios' help, the MACOs still exist. Personally I think they would work better as special abilities or maybe as a bridge officer more so than a playable character, but I wanted to throw all of the possibilities out there. I definitely think that a couple of MACOs would be better than than the two red shirts that beam down when you use the security detail ability. And for all those that think that red shirts are better, there is a reason why there are so many demotivational posters about red shirts, because they suck at combat. At least the NPCs do anyway.
I wasn't aware of the TR-116 being available. Is there another way to obtain it?